29 January 2009

Sludge on Your Veggies

"A nationwide survey of sewage treatment plants shows that the sludge they produce--the residue from cleaning up wastewater--contains a wide variety of toxic metals, pharmaceuticals, flame retardants, and other compounds, including some antibiotics in surprisingly high concentrations. That's significant because every year more than half of the roughly 7 million metric tons of these so-called biosolids produced in the United States are applied as fertilizer to farm fields."

The EPA wanted to allow sludge to be used at organic farms, but the practice is not allowed.

Bottom Line: Wash those veggies!


  1. So, what should we do with all that sludge? Spraying it on veggies is obviously not a good idea. How much does composting clean it up? Feeding it to worms?

  2. David, have you looked into the processing and treatment that goes into producing the biowaste that is permitted for use on farms? Heavy metal contamination is a concern--pathogens rarely.

  3. Jeremy and Matthew -- I don't have good answers, since I am not a scientist.

    I am guessing that the worst stuff (heavy metals) has to be separated and/or put into toxic storage. There may be some "nice" bacteria that can take care of the problem...

  4. Another timely topic since we have just been approached by a company that wants to spread it on our fields. The material and all associated transportation and application costs are free to the grower. The material has to be incorporated within 3 hours because of a new air board rule. There are a lot of restrictions on when a food crop can be planted on a field that has used sludge, so I don't see how it will be so dangerous (you should probably wash your veggies regardless). The material cannot be spread unless the analysis of the material meets certain criteria and most of the heavy metals are ND (non detectable). The limiting factor is nitrogen, because they can only apply the amount of sludge that whatever the crop is will use (PAN - Plant Available Nitrogen).

    Now that egg and chicken production will be forced out of California by Prop 2 (yes, all you who voted for it did nothing for the chickens except move them out of California), the cost of chicken manure will increase and more will look to alternative sources of organic matter and nitrogen. Keep the sludge coming!


Spam will be deleted. If you're having problems posting, email your comment to me